1. Field of The Invention
The present invention relates to an aromatic polycarbonate composition. More particularly, the present invention is concerned with an aromatic polycarbonate composition which is substantially the same as that produced by a method comprising: (1) subjecting to a transesterification reaction in a polymerizer at least one polymerizable material selected from the group consisting of a molten monomer mixture of an aromatic dihydroxy compound and a diaryl carbonate, and a molten prepolymer obtained by a process comprising reacting an aromatic dihydroxy compound with a diaryl carbonate, wherein the polymerizable material is present in the form of a liquid mass in the polymerizer, and wherein the transesterification reaction of the liquid mass of polymerizable material is performed under reaction conditions such that a specific relationship is satisfied among an evaporation surface area (m.sup.2) of the liquid mass of polymerizable material which is defined as the area (m.sup.2) of an exposed surface of the liquid mass of polymerizable material, the volume V (m.sup.3) of the liquid mass of polymerizable material in the polymerizer, and the number average molecular weight Mn of the aromatic polycarbonate to be produced, thereby obtaining an aromatic polycarbonate (A) in molten form; (2) adding to the obtained aromatic polycarbonate (A) in molten form a thermoplastic resin (B) other than an aromatic polycarbonate; and (3) kneading said aromatic polycarbonate (A) and said thermoplastic resin (B) together. The aromatic polycarbonate composition of the present invention is advantageous not only in that it can be produced in high efficiency, but also in that it is a high quality aromatic polycarbonate composition which has excellent color and which is free from occurrence of disadvantageous phenomena during the molding thereof, such as occurrence of silver streaks and a lowering of the Izod impact strength.
2. Prior Art
Aromatic polycarbonates have been known as engineering plastics having excellent heat resistance, impact resistance and transparency, and have been widely used in various fields. Particularly, in recent years, in a wide variety of fields, such as domestic electric appliances and automobiles, use has been made of various shaped articles obtained by molding an aromatic polycarbonate alloy which is produced by kneading an aromatic polycarbonate together with a resin other than an aromatic polycarbonate so as to improve the moldability and/or solvent resistance of the aromatic polycarbonate.
Conventionally, with respect to a shaped polymer alloy article produced from an aromatic polycarbonate and a resin other than an aromatic polycarbonate, the production thereof is conducted by molding a polymer alloy obtained by kneading in an extruder an aromatic polycarbonate, which is obtained by an interfacial polycondensation process using phosgene, together with a resin other than an aromatic polycarbonate. However, such a conventional shaped polymer alloy article has disadvantages as follows. The above-mentioned interfacial polycondensation process has problems in that it is necessary to use phosgene, which is poisonous, and that a reaction apparatus is likely to be corroded with chlorine-containing compounds, such as hydrogen chloride and sodium chloride, which are by-produced, and methylene chloride which is used as a solvent in a large quantity. Further, in the interfacial polycondensation process, it is difficult to separate and remove impurities, such as sodium chloride, and residual methylene chloride. When an aromatic polycarbonate containing the above-mentioned impurities and/or the above-mentioned residual methylene chloride is used to obtain a shaped polymer alloy article, the obtained article disadvantageously has poor thermal stability. Further, conventionally, in the production of the aromatic polycarbonate alloy which is conducted by melt-kneading the aromatic polycarbonate with a resin other than an aromatic polycarbonate, the aromatic polycarbonate is used in the form of pellets or powder, so that melt-kneading needs to be conducted at high temperature so as to melt the aromatic polycarbonate and the resin. As a result, problems arise such that the aromatic polycarbonate suffers heat deterioration, and that the aromatic polycarbonate alloy suffers discoloration. Further, when the aromatic polycarbonate alloy is subjected to molding to obtain a shaped article, the aromatic polycarbonate alloy undergoes heat deterioration during the molding, so that problems arise such that the obtained shaped article disadvantageously has low Izod impact strength and that the shaped article has poor appearance due to the occurrence of silver streaks.
For solving the above-mentioned problems inevitably occurring in association with the production of an aromatic polycarbonate by the interfacial polycondensation process, it has been proposed to conduct the production of an aromatic polycarbonate by melt polymerization process.
In the melt polymerization process, the aromatic polycarbonate is produced by a transesterification process, i.e., performing an ester exchange reaction between an aromatic dihydroxy (e.g., bisphenol A) and a diaryl carbonate (e.g., diphenyl carbonate) in molten state, while removing by-produced phenol. Unlike the interfacial polycondensation process, the transesterification process has an advantage in that a solvent need not be used. However, the transesterification process has a serious problem; namely, since the viscosity of the polymer being formed increases during the progress of the polymerization reaction, it becomes difficult to remove by-produced phenol from the polymerization reaction system efficiently, thus making it difficult to achieve a high degree of polymerization with respect to a polycarbonate produced. Therefore, conventionally, it has been practiced to employ a high polymerization temperature so as to lower the viscosity of the polymer being formed, thereby achieving a high degree of polymerization. In this case, however, the obtained aromatic polycarbonate has disadvantages such that the aromatic polycarbonate is discolored, that the aromatic polycarbonate has a broad molecular weight distribution so that it has poor impact resistance, and that even when the aromatic polycarbonate is mixed with a resin other than an aroma tic polycarbonate and subjected to molding, the resultant shaped article is not free from the problems, such as the discoloration, the lowering of Izod impact strength and the occurrence of silver streaks.
Various polymerizers have been known for use in producing aromatic polycarbonates by the transesterification process. A vertical agitation type polymerizer vessel equipped with an agitator is widely used. The vertical agitation type polymerizer vessel equipped with an agitator is advantageous in that it exhibits high volumetric efficiency and has a simple construction, so that polymerization on a small scale can be efficiently carried out. However, the vertical agitation type polymerizer vessel has a problem in that, as mentioned above, the by-produced phenol is difficult to remove from the polymerization reaction system efficiently in the production of aromatic polycarbonates on a commercial scale, so that the polymerization rate becomes extremely low.
Specifically, a large-scale vertical agitation type polymerizer vessel generally has a greater ratio of liquid volume to vaporization area than a small-scale one. In other words, the depth of a reaction mixture in the polymerizer is large and, hence, the pressure in the lower part of the agitation vessel is large. In such a case, even if the degree of vacuum of the polymerization reaction zone is raised in order to achieve a high degree of polymerization in the lower part of the agitation vessel, the polymerization proceeds under virtually high pressure due to the weight of the reaction mixture, so that phenol and the like cannot be efficiently removed.
To solve the above-mentioned problem, various attempts have been made to remove the by-produced phenol and the like from a high viscosity polymer being formed. For example, Examined Japanese Patent Application Publication No. 50-19600 (corresponding to GB-1007302) discloses the use of a screw type polymerizer having a vent. Examined Japanese Patent Application Publication No. 52-36159 discloses the use of an intermeshing twin-screw extruder. Examined Japanese Patent Application Publication No. 53-5718 (corresponding to U.S. Pat. No. 3,888,826) describes a thin film evaporation type reactor, such as a screw evaporator and a centrifugal film evaporator. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 2-153923 discloses a method in which a combination of a thin film evaporation type apparatus and a horizontal agitation type polymerizer vessel is used.
Of these polymerizers, horizontal polymerizers, such as a screw evaporator and a horizontal agitation type polymerizer vessel, are intended to increase, by rotary agitation, the surface renewal of polymer (being formed) to a level as high as possible in an attempt to remove phenol and the like efficiently. For example, Examined Japanese Patent Application Publication No. 50-19600 describes that "A relatively large, continuously renewing interface is formed between the liquid reaction system and the ambient gas or vapor, so that a volatile reaction product formed in the liquid reaction system is extremely smoothly removed." (see page 1, right-hand column, lines 19 to 22 of the above patent document). That is, the above patent document suggests that phenol and the like can be efficiently removed by the renewal of gas-liquid interface. Further, in Examined Japanese Patent Application Publication No. 52-36159, the surface renewal effect is defined as the functions of the screw revolution rate, the screw surface area in the reaction zone, the total screw pitch number in the reaction zone, the feed amount of a raw material and the effective volume per screw pitch in the reaction zone, and it is described that it is limited. This is because when an increase in the size of the agitation type polymerizer is intended, it is necessarily required to increase the strength of the agitator and the motive power for agitation; however, it is limited to increase such strength and motive power. Therefore, with the use of an agitation type polymerizer, the production amount of the aromatic polycarbonate cannot be easily increased. That is, agitation type polymerizers have also a problem in that a scale-up of the production of an aromatic polycarbonate is difficult.
With respect to centrifugal film evaporators, Unexamined Japanese Patent Application Laid-Open Specification No. 2-153923 has a description to the effect that, by using a centrifugal film evaporator as a polycondensation reactor in the final stage of a transesterification reaction, the evaporation surface area of the liquid reaction system per unit weight of the liquid reaction system can be increased, thereby enabling a decrease in the residence time of the liquid reaction system in the reactor. However, the above patent document also points out the following problems. When a centrifugal film evaporator is used, a part of the polymer being formed sticks to the surfaces of a driving shaft, a blade, a bearing for the driving important that the respective values of the above-mentioned parameters be in specific ranges. However, in the case of these horizontal polymerizers, a rotary agitation force produced by, for example, a screw or an agitator is needed for increasing the surface renewal. It should be noted that the viscosity of an aromatic polycarbonate being formed markedly increases in accordance with the increase in the molecular weight thereof during the polymerization reaction, so that an extremely large agitation force becomes necessary. In addition, when a large agitation force is exerted on a polymer having a high viscosity, the polymer sustains a large shearing force and, hence, a breakage of the molecular chain occurs , so that the rate of the increase of the molecular weight becomes low, leading to a difficulty in obtaining an aromatic polycarbonate having a high molecular weight. Further, when an aromatic polycarbonate sustains a large shearing force, a discoloration of the polycarbonate and a lowering of the heat resistance thereof occur, so that the quality of the aromatic polycarbonate is seriously adversely affected. Furthermore, when the production of an aromatic polycarbonate by using an agitation type polymerizer is performed on a commercial scale, the size of the agitation type polymerizer is inevitably shaft, and the like, and is exposed to a thermal experience for a long period of time, so that the sticking part of the polymer is decomposed to form a black decomposition product, and the black decomposition product undesirably enters the polymer being produced. In order to obviate this problem, the above patent document discloses a method in which a centrifugal film evaporator is not used in the final stage of the reaction, but is used in the middle stage of the transesterification reaction. However, in this method, a film of a polymer is formed only on the inner wall surface of the evaporator and, hence, the volumetric efficiency of the evaporator as a polymerizer is extremely low, so that a satisfactory reaction time cannot be obtained without using a very large reactor. Thus, the centrifugal film evaporator cannot be suitably used on a commercial scale.
As described hereinabove, in the production of an aromatic polycarbonate by the transesterification process (which is free from the problems due to impurities and residual methylene chloride), when the transesterification process is performed by conventional production methods using a vertical agitation type polymerizer, a horizontal agitation type polymerizer, a centrifugal film evaporator or the like, various other problems arise such that phenol cannot be removed efficiently, that a very large motive power for agitation is needed, that the molecular chain of a polymer being formed is broken by the shearing force due to the very large motive power for agitation, resulting in a lowering of the rate of the increase of the molecular weight and in a discoloration of the polymer, that the Izod impact strength of the produced aromatic polycarbonate becomes low, and that, since an aromatic polycarbonate experiences a long thermal history, a heat decomposition product of the aromatic polycarbonate is likely to be formed, and the thus formed heat decomposition product undesirably enters the polymer being produced, that the volumetric efficiency of a polymerizer (i.e., the ratio of the volume of a liquid reaction system in the polymerizer to the inner volume of the polymerizer) is extremely low, and that a scale-up of the production of an aromatic polycarbonate is difficult.
With respect to the production of a polymer alloy of an aromatic polycarbonate and a resin other than an aromatic polycarbonate, Unexamined Japanese Patent Application Laid-Open Specification No. 5-239331 proposes a method in which the resin is added to a molten aromatic polycarbonate obtained by the above-mentioned melt polymerization method using a combination of the centrifugal film evaporator and the horizontal agitation type polymerizer, followed by mixing. In this method, since the aromatic polycarbonate is already in a molten state at the time of mixing thereof with the resin, it is possible to alleviate the problems, such as a heat deterioration of the aromatic polycarbonate and a discoloration of the shaped polymer alloy article, which inevitably occur when the aromatic polycarbonate in the form of pellets or powder is used to obtain the aromatic polycarbonate alloy. However, by this method, it is impossible to solve the above-mentioned problems which are likely to occur during the production of the aromatic polycarbonate, such as a discoloration of the polymer, and a formation of heat decomposition products due to the long thermal history of the aromatic polycarbonate and the entry of the formed heat decomposition products into the polymer being formed. Therefore, this method has problems such that the resultant shaped polymer alloy article is poor with respect to the color and that the lowering of Izod impact strength and the silver streaks are likely to occur during the molding of the aromatic polycarbonate alloy.